Looking to contextualize recent findings of the scientific journal Science, a group of international researchers found that current trends of loss in species abundance and diversity may signal a tipping point for the Earth's sixth mass extinction event-one caused indirectly by humans' presence here on the green planet.
Lead by Professor of Biology at Stanford University, Rodolfo Dirzo, the international consortium of scientists from the Americas and Western Europe reviewed literature and analyses of data published in Science, finding alarming evidence that human activity and influence on the biosphere may lead to the first mass extinction Earth has seen not caused by catastrophic planetary events. Designating the current state as an era of "Anthropocene defaunation", for the affect that human activity has on decreases in abundance of animal species (fauna), Dirzo and his colleagues believe that outbreaks of diseases like the current Ebola epidemic in East Africa may be a sign of something even worse to come.
"Where human density is high, you get high rates of defaunation, high incidence of rodents, and thus high levels of pathogens, which increases the risks of disease transmission" Dirzo said. "Who would have thought that just defaunation would have all these dramatic consequences? But it can be a vicious circle."
In spite of the Earth currently having the highest biodiversity in the history of documented life, researchers fear that trends towards ever-decreasing species abundance in recent centuries is a warning sign that is now signaling impending disastrous ramifications for the most abundant and influential species on the planet-humans.
Since the turn of the 16th century, species abundance in nearly every vertebrate species on Earth has shown an average 25 percent decrease and more than 320 species have become extinct... and that's only what is documented. Currently between sixteen and thirty-three percent of all species are estimated to face extinction within the next century, and although many are listed as endangered species, not all receive protection nor are maintaining current population sizes.
Looking to keystone species and the effect that current trends are having on some of the largest animals, classified as "megafauna", the research team concluded that the high rates of decline match trends that led to previous mass extinctions. Also, looking into events of the last 35 years when human population doubled from 3.7 billion to 7.2 billion people, they highlighted that population sizes and species of invertebrates like many pollinators decreased by a staggering 45 percent.
And it is the loss of these few species that will ultimately lead to the collapse of humanity Dirzo says.
"We tend to think about extinction as loss of a species from the face of Earth, and that's very important, but there's a loss of critical ecosystem functioning in which animals play a central role that we need to pay attention to as well," Dirzo said. "Ironically, we have long considered that defaunation is a cryptic phenomenon, but I think we will end up with a situation that is non-cryptic because of the increasingly obvious consequences to the planet and to human wellbeing."
In decimating species that play vital roles in food production, nutrient cycling (decomposition), and keeping population sizes of vector species like rodents and pathogenic insects at bay, the review published this August in Science predicts that spread of disease will raise awareness to the ongoing mass extinction taking place, as well as the consequences additional habitat change will pose to the future of life on Earth.
